1. Field of the Invention
This invention relates to a window unit having an adapter sill plate for use in combination with an exisitng sill disposed in an opening in a building wall.
2. Prior Art
The type of exterior window units with which this invention is concerned provides a high degree of thermal insulation, air-tightness, and sound insulation since the units are mounted on the outside of openings in building walls, in which openings other window assemblies are normally present. The exterior window units of this kind have increasingly been used because they can retain a pleasing appearance of the preinstalled window assemblies having paper screen sashes (known as "Shoji" in Japan). The normally present or regular window assemblies have fixed frames made usually out of wood. Therefore, the sills of the fixed frames are prone to become worn rapidly when subjected to repeated sliding frictional movement thereon of the sashes. This has led to a drawback in that the frame sills of the exterior window units fail to fit dimensionally with the worn sills, and thus heretofore the latter must be replaced with new ones.